Adding a plastic cover over teeth (braces)
Teeth plastic braces
In short - Solidify, Remesh, Boolean modifier

I used model from Blendswap. Teeths on this model are open on bottom part. For remeshing is necessary close the mesh topology (make manifold). Go to edit mode, select all and press Fill (F). Same for Gum object, just here is better to use Grid Fill.
Add modifiers

Solidify desired thickness
Remesh &gt; Voxel &gt; Size 0.01
Boolean &gt; Difference &gt; Object &quot;Gum&quot; (decrease Threshold 0 m)

Copy Object (just for safety) and Apply modifiers (cmd+A)
Because bottom part is after boolean operation filled, go to edit mode search for Sharp Edges &gt; increase to 75 deg, press (V) Split, select one bottom face and press (L) Linked, (X) Delete
(or you can use Edge Split modifier for the same purpose)



Note:

I tried to make smooth transition between teeth, but you can make it more sharpen if you use Solidify only for the final result (so skip first Solidify and start directly with Remesh modifier).
Solidify used only at the end prevent brace to overlap gum as visible on the first image now, or use Solidify for Boolean operation on Gum object as well.
To select bottom part with Sharp Edge is a magic in this case :) Previously I spent several hours by selecting bottom part with Select Similar Co-planar that seemed to be fine but there left a lot of small parts around edge that raised as a lot of issues after Solidify on final mesh.